Project Summary: Regulatory Mechanisms of Outer Membrane Protein Expression in Helicobacter pylori Unlike most bacterial infections of the gastrointestinal tract where hosts either succumb to the infection or recover and eliminate the pathogen (e.g. Salmonella, Vibrio, Shigella), Helicobacter pylori infection of the human stomach is often a lifelong infection. The mechanisms that allow this gram-negative bacterium to persist in the human stomach for decades, even in the face of immune and inflammatory responses, have eluded the scientific community. Together with my undergraduates and masters students here at William & Mary, we investigate the determinants of regulation of outer membrane protein gene expression in response to acid and in response to contact with the host's gastric cells. Adaptation to an acid environment and to the encounter with host cells is an important step in bacterial pathogenesis. From a basic science perspective, we believe that an unusual, phosphorylation independent signal transduction mechanism we've characterized, is involved in the acid regulated gene expression in this pathogen. We contend that acid-induced repression of an adhesin gene, via a sensory histidine kinase, occurs independently of phosphorylation of the response regulator. We feel this is a solid experimental system to investigate the basis of signal transduction in H. pylori. We also intend to further characterize the impact of alternative forms of gene regulation and gene copy number variation, on oipA expression, an important outer membrane protein adhesin implicated in the host inflammatory response. We have turned oipA phase on, and thus expressed, in a strain that lacks the sine qua non of virulence; the cag Pathogenicity Island and an active (s1/m1) allele of vacuolating cytotoxin. This crucial tool will now allow us to dissect the effects of OipA on human gastric cells in vitro without the complications of these crucial virulence determinants. We have documented natural cases of gene duplication involving oipA, and our studies are designed to experimentally explore the potential effects in the production of a pro- inflammatory phenotype in some H. pylori isolates. We speculate that the decades long persistence of H. pylori infection may be, at least in part, mediated by highly complex regulation of these 30 or so outer membrane proteins. By altering the constellation of outer membrane proteins expressed and the amplitude with which each is expressed, H. pylori may circumvent the host's ability to rid the stomach of this potentially cancer causing infection.